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C. Wu

Publications and source records attributed to C. Wu.

At least 19 recordsLinked to original sources

Areal-time disruption prediction and mitigation system for the EXL-50U spherical torus

This work presents a real-time disruption prediction and mitigation system developed for high-current operations in the EXL-50U Spherical Torus. By leveraging Reflective Memory (RFM) technology, the system establishes a low-latency real-time data path, creating a fully integrated pipeline that synchronizes multi-channel diagnostic acquisition, online preprocessing, real-time inference, and Massive Gas Injection (MGI) triggering. At its core, a lightweight prediction model based on a Temporal Convolutional Network (TCN) with a channel attention mechanism extracts disruption precursor features while adaptively weighting the importance of different diagnostic channels. {Tested across discharges \#14036--\#14790, the system achieves a true positive rate of 82.4\% and a false positive rate of 16.5\%, with end-to-end latency below $1~\mathrm{ms}$ in online operation.} Mitigation experiments further show that the MGI system can supply the required gas inventory and trigger a rapid post-injection plasma response, supporting the operational requirements of EXL-50U and providing engineering guidance for future devices such as EHL-2. These results confirm the engineering feasibility of integrated real-time disruption control on EXL-50U, offering a robust basis for future research in higher-parameter fusion devices.

physics.plasm-ph

First Gamma-Ray Burst Observations with SVOM

Following its launch on 22 June 2024, the Space-based multi-band astronomical Variable Objects Monitor (SVOM) successfully completed its flight acceptance, commissioning, and scientific validation phases in early 2025, during which several tens of gamma-ray bursts (GRBs) were detected onboard. Three quarters of these events have also been detected by other satellites, and a quarter are SVOM-only GRBs. In this article, we describe these early GRB observations, with a first description of the SVOM GRB sample that is emerging, and of the level of characterisation already achieved, and with a focus on a few events of particular interest. These early results are very encouraging regarding SVOM's ability to detect and fully characterise (including prompt emission, afterglow and distance) a wide range of GRBs (classical long GRBs, short GRBs, X-Ray Flashes, etc.) and to enable the use of these extreme high-energy transients as probes of the distant Universe.

astro-ph.HE

Early results from the SVOM Observatory Science program

We present the organisation and early results from the Observatory Science program of the Space-based multi-band astronomical Variable Objects Monitor (SVOM), based on data collected between July 2024 and December 2025. Although primarily designed for gamma-ray burst studies, SVOM's wide-field, multi-wavelength instruments enable a broad range of high-energy astrophysical investigations. We summarize the execution and performance of the General Program and Target-of-Opportunity observations, and we describe the frameworks used for serendipitous source detection and monitoring with the ECLAIRs coded-mask instrument. Over this period, SVOM carried out more than a thousand pointed observations and detected several hundred non-GRB high-energy sources, mainly X-ray binaries, as well as blazars, stellar flares, magnetars, and unidentified events. We highlight some key results, including the monitoring of the microquasar Cygnus X-1, the detection of burst oscillations from the Low-Mass X-ray Binary 4U 0614+091, the spectral-state monitoring of Aql X-1, the first SVOM detection of an X-ray blazar flare from 1ES 1959+650, and observations of a stellar flare from HD 22468. These results demonstrate SVOM's strong capabilities for time-domain astrophysics beyond its core GRB program.

astro-ph.HE

Position: A Three-Layer Probabilistic Assume-Guarantee Architecture Is Structurally Required for Safe LLM Agent Deployment

This position paper argues that enforcing LLM agent safety within a single abstraction layer is not merely suboptimal but categorically insufficient for deployed LLM agents -- a structural consequence of how agent execution works, not a contingent limitation of current systems. The three dimensions that jointly constitute safe operation -- semantic intent and policy compliance, environmental validity, and dynamical feasibility -- each depend on a strictly distinct set of information that becomes available at different stages of execution. No single guardrail can certify all three. We argue that the community must respond with a contract-based architecture in which each safety dimension is enforced by an independently certified layer whose probabilistic guarantee satisfies the next layer's assumption. We sketch such an architecture and derive the compositional system-level safety bounds it admits via the chain rule of probability. Three open problems stand between this and a deployable standard: bound estimation from non-i.i.d.\ traces, graceful degradation of contracts under deployment drift, and extension to multi-agent settings -- the most important unfinished business in LLM agent runtime assurance.

cs.AI

The SVOM mission, its profile and its system

The SVOM (Space-based Variable Objects Monitor) mission, launched into low Earth orbit on 22 June 2024, is a French-Chinese multi-wavelength observatory dedicated to the study of the transient sky. Inspired by the Neil Gehrels Swift Observatory, it consists of an autonomous rapid-slewing satellite, linked in real time to several ground-based telescopes. The space segment comprises two X-ray/gamma-ray wide-field instruments (ECLAIRs and GRM) with real-time triggering capabilities combined with two narrow-field telescopes in X-ray (MXT) and in visible (VT). In addition, the SVOM collaboration has also developed a unique visible and NIR ground-based follow-up system to promptly respond to the gamma-ray transients detected on board. The core program of SVOM will provide new insights into the Gamma-Ray Burst physics by providing a homogeneous dataset covering both the prompt and afterglow emissions, as well as better studying the low luminosity and soft Gamma-Ray Burst populations. As a versatile satellite platform with fast slewing capabilities, SVOM also comprises a Target of Opportunity program and a General Program consisting in pointed observations scheduled over the year that will both significantly contribute to the multi-messenger and time-domain astronomy.

astro-ph.HE

XRF 241001A/SN 2024aiiq: A faint soft X-ray transient detected by SVOM with a broad-line type Ic supernova revealed by JWST

X-ray flashes (XRFs) are a type of gamma-ray burst (GRB) with prompt emission predominantly below 30 keV and have been poorly detected by previous missions. The advent of the SVOM mission, with its wide-field instrument ECLAIRs, provides a new way to detect soft X-ray transients. We present photometric and spectroscopic observations of XRF 241001A detected by SVOM, a soft, subluminous, and low-energetic burst located in a poorly populated region of the Amati relation. We investigated the origin of its faint, soft high-energy emission to assess its connection to the long GRB population. We analyzed the SVOM/ECLAIRs prompt emission and modeled its afterglow emission from X-ray to-radio. We present JWST/NIRSpec and SVOM/VT observations of the associated supernova (SN 2024aiiq), and we compared its properties with previously detected GRB/SNe. The event XRF 241001A is located at z = 0.573 and has a prompt emission dominated by photons below 20 keV with a duration of T90 = 3.14 seconds. Its spectrum is consistent with both thermal and nonthermal models, each implying a low Epeak < 10 keV and Eiso ~ 8x10^49 erg. The X-ray-to-radio afterglow modeling favors an origin from a relativistic jet viewed on-axis. In the optical, XRF 241001A exhibits an early blue emission, similar to that detected in some eFXTs and inconsistent with synchrotron emission. The JWST/NIRSpec observations firmly established its collapsar origin by revealing a SN Type Ic with broad lines, comparable to SN 1998bw and SN 2025kg-like events. The event XRF 241001A is a soft low-luminosity collapsar event produced by a weak relativistic jet observed on-axis, supporting the view that part of the XRF population forms the low-energy soft tail of the long GRB population. Its observation demonstrates the potential of SVOM/ECLAIRs to probe the soft regime of the high-energy transient population that remains largely unexplored.

astro-ph.HE

Multi-wavelength Study of A Superflare on RS CVn-type Star HD22468 Triggered at Hard X-ray by SVOM

Detection of stellar flares at hard X-ray is still rare at the current stage. A transient was recently detected by the hard X-ray camera, ECLAIRs onboard the SVOM mission at 11:39:01.2UT on 2025, January 09. Simultaneous monitor in the optical band on the ground by SVOM/GWAC and follow-up spectroscopy enable us to confirm that the transient is caused by a superflare on HD~22468, a RS CVn-type star. The bolometric energy released in the flare is estimated to be $\sim7.2\times10^{37}-1.7\times10^{38}\ \mathrm{erg}$. The hard X-ray spectra of the event at the peak can be reproduced by the ``apec'' model of a hot plasma with a temperature of $106^{+27}_{-22}$~MK. In the optical range, the H$\alpha$ emission-line profile obtained at $\sim1.7$ hrs after the trigger shows a bulk blueshift of $-96\pm20\ \mathrm{km\ s^{-1}}$, which can be explained by either a chromospheric evaporation or a prominence eruption. The ejected mass is estimated to be $3.9\times10^{20}$ g for the evaporating plasma, and to be $3.2\times10^{21}\ \mathrm{g}<M_{\mathrm{p}}<8.8\times10^{21}\ \mathrm{g}$ for the erupted prominence.

astro-ph.SR

SVOM discovery of a strong X-ray outburst of the blazar 1ES~1959+650 and multi-wavelength follow-up with the Neil Gehrels Swift observatory

On December 6, 2024, 1ES 1959+650, one of the X-ray brightest blazars known, underwent a high-amplitude X-ray outburst detected by SVOM, the first such discovery with this mission. The source was subsequently monitored with SVOM and Swift from December 2024 to March 2025. We report the detection and multi-wavelength follow-up of this event, and describe the temporal and spectral evolution observed during the campaign. Data from SVOM/MXT, SVOM/ECLAIRs, and Swift/XRT were analyzed with log-parabola models to track flux and spectral variability. The source was detected in a bright state over the 0.3-50 keV range. During the three months of monitoring, the X-ray flux varied significantly, showing episodes of spectral hardening at high flux levels. The spectral curvature evolved more irregularly and did not show a clear trend with flux. A shift of the Spectral Energy Distribution (SED) synchrotron peak to higher energies is seen when the flux increases. This constitutes the first blazar outburst discovered in X-rays by SVOM. The coordinated follow-up with Swift provided continuous coverage of the flare and highlights the strong complementarity of the two missions for time-domain studies of blazars. The flare shows no clear signatures of either Fermi I or Fermi II acceleration, suggesting a mixed Fermi I/II scenario.

astro-ph.HE

New insights into hydrogen-assisted intergranular cracking in nickel

We characterize the grain boundary (GB) susceptibility to hydrogen-assisted intergranular cracking in pure nickel as a function of coincident site lattice value ($\Sigma$-n), over a wide range of hydrogen concentrations (4 to 14 wppm). Cracks on the surface and within the bulk material were identified across the entire gauge region of the specimens. The susceptibility of GBs to crack initiation and propagation was evaluated by separating cracks containing single GB or multiple GBs. A larger loss in fracture strain, a smaller reduction in area, and an increase in the percentage of intergranular fracture indicated a higher degree of embrittlement at elevated hydrogen concentrations. The number of cracks was significantly higher on the surface than in the bulk for the most severe hydrogen charging conditions ($\geq$ 8 wppm), while a similar number was observed for lower concentrations. The propensity for hydrogen-assisted intergranular cracking at different types of GBs on the surface and in the bulk material was consistent, indicating that while cathodic charging can promote surface cracks, it does not significantly impact the GBs relative susceptibility. The $\Sigma$-3 boundaries were the most resistant to cracking, as evidenced by the considerably lower fraction of these GBs exhibiting intergranular cracking at all hydrogen concentrations considered. This contrasts literature findings for Ni alloys and can be explained by the segregation energies and reductions in the cohesive strength with hydrogen, with less favorable trapping at the $\Sigma$-3 boundaries. No evidence of plasticity-mediated cracking initiation was observed.

cond-mat.mtrl-sci

SVOM GRB 250314A at z $\simeq$ 7.3: an exploding star in the era of reionization

Most long Gamma-ray bursts originate from a rare type of massive stellar explosion. Their afterglows, while rapidly fading, can be initially extremely luminous at optical/near-infrared wavelengths, making them detectable at large cosmological distances. Here we report the detection and observations of GRB 250314A by the SVOM satellite and the subsequent follow-up campaign with the near-infrared afterglow discovery and the spectroscopic measurements of its redshift z $\simeq$ 7.3 . This burst happened when the Universe was only $\sim$ 5% of its current age. We discuss the signature of these rare events within the context of the SVOM operating model, and the ways to optimize their identification with adapted ground follow-up observation strategies.

astro-ph.HE

Picking-up Local GRB Candidates Based on Their Host Galaxies

Rapid identification of candidates of high-value gamma-ray bursts (GRBs), including both high-$z$ and local events, is crucial for outlining subsequent observational strategy. In this paper, we present a model that enables an on-duty astronomer to rapidly identify candidates of local GRBs prior to spectroscopy, provided that these events have been localized at an arcseconds precision. After taking into account the mass distribution of the host galaxies of GRBs, the model calculates the two-dimensional cross-match probabilities between a localized GRB and its surrounding nearby galaxies, and then returns the best match with the highest probability. The model is evaluated not only by the observed GRB sample with redshifts up to $z=4$, but also through the simulated GRB samples. By using the recently published GLADE+ galaxies catalog with a completeness of 95\% up to 500Mpc, along with the NED-LVS catalog, the Precision and Recall of the model are determined to be 0.23-0.33 and 0.75, respectively, at the best performance. A dedicated web service, which will be integrated into the SVOM Science User Support System, has been developed to deploy the model.

astro-ph.HE

Potential Chromospheric Evaporation in A M-dwarf's Flare Triggered by Einstein Probe Mission

Although flares from late-type main-sequence stars have been frequently detected in multi-wavelength, the associated dynamical process has been rarely reported so far. Here, we report follow-up observations of an X-ray transient triggered by WXT onboard the Einstein Probe at UT08:45:08 in 2024, May 7. The photometry in multi-bands and time-resolved spectroscopy started at 3 and 7.5 hours after the trigger, respectively, which enables us to identify the transient as a flare of the M-dwarf 2MASS J12184187-0609123. The bolometric energy released in the flare is estimated to be $\sim10^{36}\ \mathrm{erg}$ from its X-ray light curve. The H$\alpha$ emission-line profile obtained at about 7 hours after the trigger shows an evident blue asymmetry with a maximum velocity of $200-250\ \mathrm{km\ s^{-1}}$. The blue wing can be likely explained by the chromospheric temperature (cool) upflow associated with chromospheric evaporation, in which the mass of the evaporating plasma is estimated to be $1.2\times10^{18}$g. In addition, a prominence eruption with an estimated mass of $7\times10^{15}\mathrm{g}<M_{\mathrm{p}}<7\times10^{18}\mathrm{g}$ can not be entirely excluded.

astro-ph.SR

The Lobster Eye Imager for Astronomy Onboard the SATech-01 Satellite

The Lobster Eye Imager for Astronomy (LEIA), a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe (EP) mission, was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on 27 July 2022. In this paper, we introduce the design and on-ground test results of the LEIA instrument. Using state-of-the-art Micro-Pore Optics (MPO), a wide field-of-view (FoV) of 346 square degrees (18.6 degrees * 18.6 degrees) of the X-ray imager is realized. An optical assembly composed of 36 MPO chips is used to focus incident X-ray photons, and four large-format complementary metal-oxide semiconductor (CMOS) sensors, each of 6 cm * 6 cm, are used as the focal plane detectors. The instrument has an angular resolution of 4 - 8 arcmin (in FWHM) for the central focal spot of the point spread function, and an effective area of 2 - 3 cm2 at 1 keV in essentially all the directions within the field of view. The detection passband is 0.5 - 4 keV in the soft X-rays and the sensitivity is 2 - 3 * 10-11 erg s-1 cm-2 (about 1 mini-Crab) at 1,000 second observation. The total weight of LEIA is 56 kg and the power is 85 W. The satellite, with a design lifetime of 2 years, operates in a Sun-synchronous orbit of 500 km with an orbital period of 95 minutes. LEIA is paving the way for future missions by verifying in flight the technologies of both novel focusing imaging optics and CMOS sensors for X-ray observation, and by optimizing the working setups of the instrumental parameters. In addition, LEIA is able to carry out scientific observations to find new transients and to monitor known sources in the soft X-ray band, albeit limited useful observing time available.

astro-ph.IM

Using birth-death processes to infer tumor subpopulation structure from live-cell imaging drug screening data

Tumor heterogeneity is a complex and widely recognized trait that poses significant challenges in developing effective cancer therapies. In particular, many tumors harbor a variety of subpopulations with distinct therapeutic response characteristics. Characterizing this heterogeneity by determining the subpopulation structure within a tumor enables more precise and successful treatment strategies. In our prior work, we developed PhenoPop, a computational framework for unravelling the drug-response subpopulation structure within a tumor from bulk high-throughput drug screening data. However, the deterministic nature of the underlying models driving PhenoPop restricts the model fit and the information it can extract from the data. As an advancement, we propose a stochastic model based on the linear birth-death process to address this limitation. Our model can formulate a dynamic variance along the horizon of the experiment so that the model uses more information from the data to provide a more robust estimation. In addition, the newly proposed model can be readily adapted to situations where the experimental data exhibits a positive time correlation. We test our model on simulated data (in silico) and experimental data (in vitro), which supports our argument about its advantages.

q-bio.PE

CFD simulation for Hydraulic Short-Circuit feasibility analysis

Hydraulic Short Circuit (HSC) application allows the simultaneous pumping and generating operations on different units of the same pumped hydro energy storage (PHES) plants for the extension of the power consumption range. This article proposes a methodology based on time-history statistics and CFD numerical simulations to investigate the feasibility of integrating such a kind of operation in pre-existing hydropower plants. The evaluation of the potential power output and pressure drop analysis in the new HSC operation are presented. The penstock trifurcation of a selected PHES plant is also analysed by CFD simulations, by evaluating the loss-head coefficients and comparing the flow conditions in different PHES operations.

physics.flu-dyn

Deep Learning Enables Reduced Gadolinium Dose for Contrast-Enhanced Blood-Brain Barrier Opening

Focused ultrasound (FUS) can be used to open the blood-brain barrier (BBB), and MRI with contrast agents can detect that opening. However, repeated use of gadolinium-based contrast agents (GBCAs) presents safety concerns to patients. This study is the first to propose the idea of modeling a volume transfer constant (Ktrans) through deep learning to reduce the dosage of contrast agents. The goal of the study is not only to reconstruct artificial intelligence (AI) derived Ktrans images but to also enhance the intensity with low dosage contrast agent T1 weighted MRI scans. We successfully validated this idea through a previous state-of-the-art temporal network algorithm, which focused on extracting time domain features at the voxel level. Then we used a Spatiotemporal Network (ST-Net), composed of a spatiotemporal convolutional neural network (CNN)-based deep learning architecture with the addition of a three-dimensional CNN encoder, to improve the model performance. We tested the ST-Net model on ten datasets of FUS-induced BBB-openings aquired from different sides of the mouse brain. ST-Net successfully detected and enhanced BBB-opening signals without sacrificing spatial domain information. ST-Net was shown to be a promising method of reducing the need of contrast agents for modeling BBB-opening K-trans maps from time-series Dynamic Contrast-Enhanced Magnetic Resonance Imaging (DCE-MRI) scans.

q-bio.QM

Constrains on optical emission of FAST-detected FRB 20181130B with GWAC synchronized observations

Multi-wavelength simultaneous observations are essential to the constraints on the origin of fast radio bursts (FRBs). However, it is a significant observational challenge due to the nature of FRBs as transients with a radio millisecond duration, which occur randomly in the sky regardless of time and position. Here, we report the search for short-time fast optical bursts in the GWAC archived data associated with FRB 20181130B, which were detected by the Five Hundred Meter Spherical Radio Telescope (FAST) and recently reported. No new credible sources were detected in all single GWAC images with an exposure time of 10 s, including image with coverage of the expected arrival time in optical wavelength by taking the high dispersion measurements into account. Our results provide a limiting magnitude of 15.43$\pm0.04$ mag in R band, corresponding to a flux density of 1.66 Jy or 8.35 mag in AB system by assuming that the duration of the optical band is similar to that of the radio band of about 10 ms. This limiting magnitude makes the spectral index of $\alpha<0.367$ from optical to radio wavelength. The possible existence of longer duration optical emission was also investigated with an upper limits of 0.33 Jy (10.10 mag), 1.74 mJy (15.80 mag) and 0.16 mJy (18.39 mag) for the duration of 50 ms, 10 s and 6060 s, respectively. This undetected scenario could be partially attributed to the shallow detection capability, as well as the high inferred distance of FRB 20181130B and the low fluence in radio wavelength. The future detectability of optical flashes associated with nearby and bright FRBs are also discussed in this paper.

astro-ph.HE

The GLEAM 200 MHz Local Radio Luminosity Function for AGN and Star-forming Galaxies

The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) is a radio continuum survey at 76-227 MHz of the entire southern sky (Declination $<+30\deg$) with an angular resolution of $\approx 2$ arcmin. In this paper, we combine GLEAM data with optical spectroscopy from the 6dF Galaxy Survey to construct a sample of 1,590 local (median $z \approx 0.064$) radio sources with $S_{200\,\mathrm{MHz}} > 55$ mJy across an area of $\approx 16,700~\mathrm{deg}^{2}$. From the optical spectra, we identify the dominant physical process responsible for the radio emission from each galaxy: 73 per cent are fuelled by an active galactic nucleus (AGN) and 27 per cent by star formation. We present the local radio luminosity function for AGN and star-forming galaxies at 200 MHz and characterise the typical radio spectra of these two populations between 76 MHz and $\sim 1$ GHz. For the AGN, the median spectral index between 200 MHz and $\sim 1$ GHz, $\alpha_{\mathrm{high}}$, is $-0.600 \pm 0.010$ (where $S \propto \nu^{\alpha}$) and the median spectral index within the GLEAM band, $\alpha_{\mathrm{low}}$, is $-0.704 \pm 0.011$. For the star-forming galaxies, the median value of $\alpha_{\mathrm{high}}$ is $-0.650 \pm 0.010$ and the median value of $\alpha_{\mathrm{low}}$ is $-0.596 \pm 0.015$. Among the AGN population, flat-spectrum sources are more common at lower radio luminosity, suggesting the existence of a significant population of weak radio AGN that remain core-dominated even at low frequencies. However, around 4 per cent of local radio AGN have ultra-steep radio spectra at low frequencies ($\alpha_{\mathrm{low}} < -1.2$). These ultra-steep-spectrum sources span a wide range in radio luminosity, and further work is needed to clarify their nature.

astro-ph.GA